1. Field of Inventions
The present inventions relate generally to medical devices that support one or more diagnostic and/or therapeutic elements in contact with body tissue that is associated with, for example, body orifices or lumens.
2. Description of the Related Art
There are many instances where diagnostic and/or therapeutic elements (collectively “operative elements”) must be inserted into the body to, for example, map and/or ablate body tissue. One instance involves the treatment of cardiac conditions such as atrial fibrillation, atrial flutter and ventricular tachycardia, which lead to an unpleasant, irregular heart beat, called arrhythmia. Atrial fibrillation, flutter and ventricular tachycardia occur when anatomical obstacles in the heart disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called “conduction blocks”) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called “reentry circuits,” disrupt the normally uniform activation of the chambers within the heart. Treatment of these cardiac conditions frequently involves mapping and ablation of tissue within the heart.
A variety of minimally invasive electrophysiological procedures employ catheters that position one or more operative elements adjacent to the target tissue region within the heart. Such catheters are relatively long and flexible shaft and carry the operative elements at or near their distal end. The proximal end of the catheter is connected to a handle which may or may not include steering controls for manipulating the distal portion of the catheter. The length and flexibility of the catheter allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart where the operative elements contact the tissue that is to be mapped and/or ablated. Fluoroscopic imaging may be used to provide the physician with a visual indication of the location of the catheter. Exemplary catheters are disclosed in U.S. Pat. Nos. 6,013,052, 6,203,525, 6,214,002 and 6,241,754.
One cardiac area that has proven difficult to treat with conventional catheters is the pulmonary veins. For example, ectopic atrial fibrillation may be cured by forming circumferential lesions in the antrum or ostium of pulmonary veins that include an arrhythmogenic foci. The portion of the catheter that carries the operative elements must be properly positioned relative to the pulmonary vein, and must remain in the proper position, for effective mapping and ablation of the pulmonary vein to proceed. The present inventors have determined that, with respect to positioning relative to a pulmonary vein, conventional catheters are susceptible to improvement.